James Gurney

This daily weblog by Dinotopia creator James Gurney is for illustrators, plein-air painters, sketchers, comic artists, animators, art students, and writers. You'll find practical studio tips, insights into the making of the Dinotopia books, and first-hand reports from art schools and museums.

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Wednesday, June 23, 2010

A centrolinead is a perspective tool with adjustable Y-shaped legs branching from a main bar. The legs rest against two nails placed on the drawing board.As it pivots up and down, the main bar changes slope. The resulting lines orient to a remote vanishing point that would be otherwise difficult to establish.

E.G. Lutz’s book Practical Drawing includes the diagram above.

Concept artist and illustrator Craig Elliott discovered an antique centrolinead dating from around 1890 (below). Note how the Y-legs branch from a point along the top line of the ruler. He reports:

“I did a little building facade and some windows to test out the Centrolineaid. It is such a breeze, even better than using a long ruler! I set the map pins at 3 inches from the HL and the blades at 30 degrees.

I did the verticals with a t-square and the 30-60 triangle shown. I think two or three of these would make darn quick work of a two- or three-point perspective drawing on a quite small drawing board. This board is about 24 x 32. Another benefit of this tool seems to be that it doesn't pop off the pin all the time like a regular ruler would- it is very steady on the 2 pins.

For the pins or nails, I used a paper clip with one end bent up, or even an upside down flat headed thumbtack taped to the board or paper. This is good for balancing a ruler on for perspective points on the board or for this operation.

You could also use a sheet of metal to draw on, even with a Borco cover, and Neodymium magnets about 1/2 cube size for the pins. They are so strong they won't shift.”

22 comments:

Why am I only hearing about this now? Great tip! (Although, I must admit, I do much of my perspective on the computer now.) Also, good call on the magnets. I draw on a slanted, metal board and have magnets attached to all my tools—my eraser never makes it to the floor anymore.

Digging around a little bit, I came up with this:http://books.google.com/books?id=FetJAAAAMAAJ&pg=PA43#v=onepage&q&f=false

He mentions that the two arms are adjusted 'by trial,' and that 'the difficulty of adjustment' is a problem.

Also the author leaves a tantalizing clue about the priciple on which it acts and 'a simpler instrument for the same purpose' that can be found at another resource. I'll leave that discovery for another commenter.

I was very lucky not too long ago when I came across a Klok Perspector table top. IIt did not come with the specially cut t-square that follows the bowed curve cut into the table top but all the lines and measurements are still very viewable and I got it for free!

Along with this the original purchase was for an Italian made pedestal with hydraulic lift center drawing table for $10.00!!! I learned when new this item is around a grand.

I still haven't figured out how to use the top for perspective drawing yet but what a find!

I think that with modern materials (thinner rigid plastics) you could have the 'Y' arms coming directly off the main rule instead of off a 'T'. This would allow for a wider range for the tool. In extreme angles, the tool won't work as constructed.

In his book "Architectural Rendering in Tempera" Richard Baehr, a one time well known Architectural Illustrator, provides instructions and specs on how to make a centrolinead out of metal. I bought the book in 2001 and had a metal shop make up 5 of them for me. I sold 2 of them to an Architectural Illustrator friend of mine. I never did use them as I started using SketchUp for my perspectives. SketchUp conveniently prints large perspectives on tile sheets of paper which can be taped together and transferred onto watercolor paper or whatever. The book is now available as an Ebook here: http://www.ebooknetworking.net/books_detail-0471285129.html

I have collected some information about the math behind the centrolinead and a few methods for setting the angles on the rulers. It helped me to understand that the vanishing point, the studs and the ruler 'elbow' all lie on a circle. You can find it here.

My husband made me one for Christmas--It takes me a while to get the arms and the pegs adjusted, but once I get it set it works great. The explanations in the old books are not for the mathematically challenged.

About 34 years ago I got a job at the research department of a famous film manufacturer as a perspective draftsman. Goal was to make perspective drawings of new machinery to show financiers what the department was trying to accomplish, and thus, to get the funds to continue... I found a tool that made it possible to create perspective drawings on a drawing-board with vanishing points lying far beyond the limits of the board itself. It consisted of a transparent plastic ruler and a booklet with some formulas... (calculator was needed!) The ruler was tapered to one end and had kind of a protractor at the other end. Logarithmic scales on all sides, and a small pinhole at the center of the protractor to fix the ruler on your drawing-board, on top off a plan-view of the object you wanted to draw. With the formulas, you could calculate all the needed points and copy them from the ruler to your drawing. In time, moving to other counties and switching lives I lost the ruler. Went back to the store where I bought it, but they don't recall of such a device. Anybody got any idea about this "perspector"? at least, that's the name by which I remembered the ruler...

This method works the same way, but you have to cut a new set of curved boards for the t-square to ride on everytime you want to change your vanishing point. The centrolinead looks to be more convenient to use.